1. Field of the Invention
The present invention relates to mechanical presses and more particularly to adjustment of the press drive and corresponding alteration of the slide displacement vs. gear angle curve without disassembly.
2. Description of the Related Art
Mechanical presses of the type performing stamping and drawing operations employ a conventional construction that includes a frame structure having a crown and a bed portion and which supports a slide in a manner enabling reciprocating movement toward and away from the bed. A press drive assembly including a main gear and a crankshaft is arranged to convert rotary-oscillatory motion into the rectilinear reciprocating motion of the slide. These press machines are widely used for a variety of workpiece operations employing a large selection of die sets, with the press machine varying considerably in size and available tonnage depending on its intended use.
Mechanical presses, such as stamping presses and drawing presses, are provided a main gear which imparts rotational motion to a crankshaft. The crankshaft has an eccentric portion, or an eccentric crank link which translates the rotational motion of the crankshaft into reciprocal mechanical activity that is transmitted to the slide through a connecting arm. One complete rotation of the crankshaft produces one complete reciprocating motion of the slide.
Depending upon the type of drive mechanism utilized, the crankshaft can maintain a constant rotational velocity or an irregular rotational velocity. Irregular rotational velocity of the crankshaft is advantageous in press applications wherein reduction of the slide velocity near the bottom of the stroke (i.e. bottom dead center) is required so that the draw speed of the material is not exceeded. Additionally, slide velocity reduction near the bottom of the stroke reduces die wear, press vibration and noise. Presses which utilize different arrangements to produce irregular rotational velocity of the crankshaft are known in the art.
A standard press arrangement which produces constant rotational velocity of the crankshaft consists of a crankshaft and main gear arrangement wherein the crankshaft and main gear are concentric. Irregular rotational velocity of the crankshaft of a mechanical press can be achieved by differing arrangements of the crankshaft and the main gear wherein the crankshaft and the main gear are eccentric and are connected by a link drive assembly. Arrangements such as a link drive create an irregular rotational velocity which is beneficial in that they can be utilized to reduce the velocity of the slide near bottom dead center so that the draw speed of a particular material is not exceeded. Such arrangements are additionally beneficial in that they reduce die wear, press vibration and noise.
Presses utilizing similarly sized main gears may be more suitable for a particular workpiece depending upon whether a link drive or a slider crank drive arrangement is used. The ability to alter the drive mechanism of a mechanical press from a slider crank drive to differing link drive arrangements is advantageous in that one particular press may be utilized for different operations. The desire to create a flexible use mechanical press has led to modular type units being utilized. These modular unit presses allow for differing drive mechanisms to be inserted so that the press will operate as a pure slider crank drive or alternatively as a link type drive. Different modular units may be used to create different link drive arrangements and geometries. That is to say, link drive arrangements in which the distance between the center line of the crankshaft and the center line of the main gear is different as well as utilizing links of variable length. The distance between the center line of the main gear and the center line of the crankshaft as well as link lengths will be varied depending upon the modular unit chosen, but will be variable only at steps defined by the particular modular units manufactured and utilized.
The ability to vary the drive of a press in this way makes the press more versatile in its application, however, having to stop the press for a long period of time to make this adjustment is problematic. Press down time is experienced while drive mechanisms are exchanged. Room to store a number of modular units must also be provided. Additionally, the space in which the press resides must provide enough room above the crown so that different drive mechanisms may be removed and inserted. Currently, the purchaser of a press must utilize the drive mechanism with which the press is initially equipped or must utilize a press which offers different modular drive units and experience the problems mentioned above.